According to the commit abd20cb637008da9d32018b4b03973e119388a0a, an
intersting thing is that - the more relax passes, the more chances of
relaxations are reduced [1]. Originally, we set the boolean `again`
to TRUE once the code is actually deleted, and then we run the relaxations
repeatedly if `again` is still TRUE. But `again` only works for the
relax pass itself, and won't affect others. That is - we can not use
`again` to re-run the relax pass when we already enter into the following
passes (can not run the relax passes backwards). Besides, we must seperate
the PCREL relaxations into two relax passes for some reasons [2], it make
us lose some relax opportunities.
This patch try to fix the problem, and the basic idea was come from Jim
Wilson - we use a new boolean, restart_relax, to determine if we need to
run the whole relax passes again from 0 to 2. Once we have deleted the
code between relax pass 0 to 2, the restart_relax will be set to TRUE,
we should run the whole relaxations again to give them more chances to
shorten the code. We will only enter into the relax pass 3 when the
restart_relax is FALSE, since we can't relax anything else once we start
to handle the alignments.
I have passed the gcc/binutils regressions by riscv-gnu-toolchain, and
looks fine for now.
[1] https://sourceware.org/pipermail/binutils/2020-November/114223.html
[2] https://sourceware.org/pipermail/binutils/2020-November/114235.html
bfd/
* elfnn-riscv.c (riscv_elf_link_hash_table): New boolean restart_relax,
used to check if we need to run the whole relaxations from relax pass 0
to 2 again.
(riscv_elf_link_hash_table_create): Init restart_relax to FALSE.
(_bfd_riscv_relax_align): Remove obsolete sec_flg0 set.
(_bfd_riscv_relax_delete): Set again to TRUE if we do delete the code.
(bfd_elfNN_riscv_restart_relax_sections): New function. Called by
after_allocation to check if we need to run the whole relaxations again.
(_bfd_riscv_relax_section): We will only enter into the relax pass 3 when
the restart_relax is FALSE; At last set restart_relax to TRUE if again is
TRUE, too.
* elfxx-riscv.h (bfd_elf32_riscv_restart_relax_sections): Declaration.
(bfd_elf64_riscv_restart_relax_sections): Likewise.
ld/
* emultempl/riscvelf.em (after_allocation): Run ldelf_map_segments many
times if riscv_restart_relax_sections returns TRUE.
* testsuite/ld-riscv-elf/restart-relax.d: New testcase. Before applying
this patch, the call won't be relaxed to jal; But now we have more chances
to do relaxations.
* testsuite/ld-riscv-elf/restart-relax.s: Likewise.
* testsuite/ld-riscv-elf/ld-riscv-elf.exp: Updated.
This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.
README for LD
This is the GNU linker. It is distributed with other "binary
utilities" which should be in ../binutils. See ../binutils/README for
more general notes, including where to send bug reports.
There are many features of the linker:
* The linker uses a Binary File Descriptor library (../bfd)
that it uses to read and write object files. This helps
insulate the linker itself from the format of object files.
* The linker supports a number of different object file
formats. It can even handle multiple formats at once:
Read two input formats and write a third.
* The linker can be configured for cross-linking.
* The linker supports a control language.
* There is a user manual (ld.texi), as well as the
beginnings of an internals manual (ldint.texi).
Installation
============
See ../binutils/README.
If you want to make a cross-linker, you may want to specify
a different search path of -lfoo libraries than the default.
You can do this by setting the LIB_PATH variable in ./Makefile
or using the --with-lib-path configure switch.
To build just the linker, make the target all-ld from the top level
directory (one directory above this one).
Porting to a new target
=======================
See the ldint.texi manual.
Reporting bugs etc
===========================
See ../binutils/README.
Known problems
==============
The Solaris linker normally exports all dynamic symbols from an
executable. The GNU linker does not do this by default. This is
because the GNU linker tries to present the same interface for all
similar targets (in this case, all native ELF targets). This does not
matter for normal programs, but it can make a difference for programs
which try to dlopen an executable, such as PERL or Tcl. You can make
the GNU linker export all dynamic symbols with the -E or
--export-dynamic command line option.
HP/UX 9.01 has a shell bug that causes the linker scripts to be
generated incorrectly. The symptom of this appears to be "fatal error
- scanner input buffer overflow" error messages. There are various
workarounds to this:
* Build and install bash, and build with "make SHELL=bash".
* Update to a version of HP/UX with a working shell (e.g., 9.05).
* Replace "(. ${srcdir}/scripttempl/${SCRIPT_NAME}.sc)" in
genscripts.sh with "sh ${srcdir}..." (no parens) and make sure the
emulparams script used exports any shell variables it sets.
Copyright (C) 2012-2021 Free Software Foundation, Inc.
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.
ebdcad3fdd